Television camera tube



PIC 70M? El 'lV/ENT TE 19/7519 T. C. KING ET AL I TELEVISION CAMERA TUBE Filed Oct. 25, 1946 Dec. 6, 1949 INVENTORS THOMAS 0. KING Wu F JAMES EDRUMMOND Patented Dec. 6, 1949 TELEVISION CAMERA TUBE Thomas C. King, Tucson, Ariz., and James Drummond, Portland, Oreg.

Application October 23, 1946, Serial No. 705, 11.6

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) 4 Claims.

This invention relates to storage type television pick-up tubes and more particularly to tubes of the icono'scope type.

It has been shown that the lower limit of illumination of a television pick-up tube which will produce a useful output in a television system is limited by the signal to mask ratios at the output of, the pick-u tube.

Masking voltages have a random nature and are generated by thermal agitation in resistors, shot eifects in video amplifiers and stray pickup. For a given system they will have a definite value. Therefore any increase of the video signal at the output of the pick-up tube without corresponding increase in masking voltages will be of direct value.

The iconoscope type of television pick-up tubes is limited in its attainable amplification by the effectiveness of present photoemissive substances. It also has a major disadvantage in that shading correction signal generators are necessary to cancel the effects of stray secondary electrons.

It is therefore an object of our invention to provide a new and useful improvement of the basic iconoscop'e tube whereby a very highly amp'lified output is obtained, and the necessity for shading correction is eliminated.

This amplified output will directly multiply the signal to mask ratio, thereby the lower limit of illumination to which this tube will respond will be cut to a fraction of the value which is now considered useful.

A further object of our invention is to provide a television pick-up tube which will be responsive to light or other related electromagnetic wave images.

In the attainment of the foregoing objects an important feature of this invention consists of the provision in a mosaic which serves as the control grid of a conventional vacuum tube.

Another important feature of this invention is the means whereby the cathode ray beam is caused to scan the aforementioned control grid.

This invention can best be understood by reference to the accompanying drawings and the description thereof.

Figure 1 is a schematic view suitably embodying the invention.

Figure 2 illustrates an alternate method of producing the deflection necessary for the tubes operation.

Fig. 3 illustrates a magnified view of a portion of the control grid I4 of Figure 1 showing thereon the electron beam area, or picture element area.-

cathode.

- 2 Figure 4 illustrates a further magnified crosssection taken on the line 4-4 of Figure 3. Referring particularly to Figure 1 there is shown a highly evacuated closed glass bulb 3 containing; an electron gun comprising a heater element a, a cathode 5, a first control grid 6, a first anode i, and a second anode 8; two pairs of juxtaposed deflection plates 9, I0 a lightly metalplated transparent plate I 2; a post deflection ac celeration ring I3; a mosaic in the form of a second control grid 14; a screen grid I5; a suppressor grid it; an output anode ll; a load re-' sistor is; an output terminal 23; and suitable sources of power l9 and 25 connected to the elements in the conventional manner illustrated in from the cathode 5 and focused into a low veloc ity beam by the combined action of the first control grid 6, the first anode and the second anode 8.

This so formed beam then passes through a pair of juxtaposed deflection plates 9 and then through another pair of juxtaposed deflection plates Ill, said pairs of plates when energized by a voltage of proper waveform will introduce a scanning motion in said beam.

The transparent plate 12 is inserted at such an angle to the scanning electron beam that, by virtue of a highly negative potential impressed thereon, by previous scanning of the electron beam the electron beam will be reflected parallel to the main body of the tube toward the output anode IT. This reflected beam is then accelerated onto the mosaic by the positive potential on the post deflection acceleration ring I3.

The aforementioned scanning electron beam, as it scans the mosaic l4 functions as a virtual This result is effected by making the mosaic or second control grid l4 negative with respect to cathode 5 and the anode l1 positive with respect to cathode 5 as shown in Figure 1. Thus the second control grid l4, screen grid [5, suppressor grid l6 and output anode I l oper ated in conjunction with said virtual cathode 3 form the elements of a conventional pentode arranged in a new manner. As previously explained, the light impinging on the mosaic l4 leaves a positive voltage pattern of varying magnitude distributed over the surface thereof which is a reproduction of the picture focussed thereon. Thus, at points on mosaic M where the positive voltage is high, more electrons from the electron beam will be repelled back to ring electrode l3 so that fewer will pass through the mesh of mosaic l4 than at points where the voltage is low, and this will cause the electron beam passing therethru to fluctuate accordingly thereby producing an electrical output voltage across the load resistor 18 which will have been amplified many times by pentode action. The electrons, as in all pentodes, will be travelling quite slowly, so that there will be practically no emission of secondary electrons thus eliminating the ne-' cessity for shading correction.

While the second control grid or mosaic I4 is hereinafter described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made without actually departing from the basic idea of the second control grid I 4.

This second control grid I4 is to be constructed of wire screen of fineness on the order of 325- mesh. For instance, the size of said grid may be four by five inches and since about 300,000 picture elements are required for good definition in a televised picture, this will mean each element of picture will encompass approximately the area of seven openings on the control grid, as illustrated in Figure 3. It is assumed that the electron beam will have a diameter of one picture element at the control grid M. This means that the beam in scanning said grid will be covering several openings at a time and will pass gradually from one opening to another thereby minimizing the masking voltage caused by the partitions between screen interstices.

The beam, in scanning the control grid mesh, however, will produce a definite frequency of masking voltage. Since there will be 325 openings per inch of horizontal scan and there are five inches of scan and since there are, with present standards, only about five hundred active horizontal lines, each line must contain about 600.0

picture elements or a little more than one-third of the 1,610 openings per line. Thus the masking voltages will be at a definite frequency possibly between two and a half and three times the frequencies encountered in passing over the maximum number of picture elements. l his masking voltage may be easily filtered out.

The sensitive material coating as illustrated in Figure 4, is not limited to photoemission substances. Photovoltaic, photoconductive, thermoconductive and thermovoltaic substances may be used as well.

For photovoltaic coatings one side of the substance will be connected directly to the wire mesh, without insulating material between as would be used for photoemissive substances. When a light picture is focused on this type coated grid, a corresponding voltage picture will be produced thereon. This voltage picture will influence the electron flow in the same manner as the previously mentioned photoemissive coated grid.

The grid may be coated with a photoconductive or a thermoconductive material and operated positively. The electrons which will flow through said coating will produce a voltage drop and thus influence the other electrons in the beam. Said 4 material will be of such a nature as to have its resistance controlled by the light or heat picture focused thereon.

In the case of thermovoltaic substances, tiny thermocouples, using the grid as one of the metals may be formed on the grid and insulated from each other. The same results would then be obtained when an infra-red, heat, or very high frequency radio wave picture was focused on a photovoltaic substance.

The screen grid I5 and suppressor grid l1 following the control grid will be used to perform the functions that are generally performed by these grids in pentode. They may, of course, in some designs of this tube, be merely aquadag coatings on the inside of the bulb or they may be dispensed with altogether to form a triode amplifier.

In Figure 2 there is shown in addition to those parts already described a coil 20 and another coil 2|. In the previous illustration the electron beam was deflected down the main body of the tube towards the output anode l! by means of a negative voltage on the deflection plate l2. This deflection is now to be accomplished by the magnetic field produced when a suitable voltage is applied to said coils 20 and 2|,

By the use of a magnetic field to produce the desired deflection it is possible to produce part or all of the scanning motion of the electron beam by another magnetic field superimposed thereon and thereby eliminating either one or both pairs of deflection plates 9 and i0.

Referring again to Figure 1, it will be noted that the neck of the tube containing the electron gun and deflecting mechanism may be set at any angle 22 other than as shown in the drawing. Thus it would be possible to dispense with the deflecting plate l2 or coils 20, 2| and allow the beam to strike the grid at an oblique angle direct from the electron gun if provision is made to control the electrons after they leave the grid.

This invention herein described and claimed may be used and/or manufactured by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.

What is claimed is:

1. A television pick-up tube comprising means for producing a scanning beam of charged particles, means for deflecting said beam, and a radiation sensitive mosaic disposed in the path of said beam to modulate said beam in accordance with the intensity of radiation on the mosaic, vacuum tube elements in said pick-up tube, said mosaic functioning as the control grid of said vacuum tube elements.

2. A multi-element television pick-up and amplifier tube having means for producing an electron beam, means for producing a transparent conductive scanning motion of said beam, a deflector plate, an accelerator ring, a radiation responsive control grid and an anode, said deflector plate being angularly disposed with respect to said electron beam to deflect said beam through said ring, said ring having a positive potential impressed thereon to accelerate said electron beam in the direction of said control grid, said control grid modulating the electrons passing therethrough to said anode at a rate dependent upon the distributed potential thereon, said potentialbeing a function of the intensity of the radiation impinging upon said control grid.

3. A multi-element television pick-up and amplifier tube comprising a cathode, a first control grid, a first and a second anode, an electromagnetic coil, an accelerator ring, a second control grid, a screen grid, a suppressor grid and an output anode, said cathode providing a source of electrons which are propelled away from said cathode and focused into a beam by said first control grid and the first and second anodes, said coil having a current applied thereto to produce a scanning motion of said beam and to deflect said beam through said ring, said ring having a positive potential impressed thereon to accelerate said beam onto said control grid which is adapted to permit the passage of electrons therethru at a rate dependent upon the distributed potential thereon, said potential being a function of the intensity of the light impinging on said grid, said electron being then acted upon by said screen grid and said suppressor grid that it is a highly amplified video signal with high signal to mask ratio when it reaches said output anode.

6 4. The tube of claim 1 in which the means for producing a scanning motion of the beam comprises a first electromagnetic coil surrounding the beam and the means for deflecting the beam comprises a second electromagnetic coil surrounding the beam and at an angle to the plane of said first electromagnetic coil.

THOMAS C. KING.

JAMES E. DRUMMOND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

